1. Field of the Invention
The present invention relates to the technical field of musical harmony recognition, and in particular, the present invention relates to an apparatus and a method for determining a type of chord using a reference vector for a key of the type of chord.
2. Description of Prior Art
In the last ten years, due to the clearly improved storage and sound optimization of recorded pieces of music, the importance of classifying these pieces of music into styles of music has increased. However, it has had to be taken into account that in the last few years a multitude of subtypes of styles of music have formed, a classification into, for example, the styles of music of “classical music”, “jazz”, “rock music”, . . . having proven to be no longer sufficient. In addition, one has had to bear in mind/to note that due to the considerable increase of pieces of music published, the formation of different tastes in music has also been boosted. The increase in the number of different tastes in music, and the marked increase of pieces of music published necessitated also a pre-classification of the pieces of music which is then enclosed, in an electronic form, as meta data (i.e. data about data) with the piece of music which was mostly also stored in an electronic form. Since the classification of the piece as may be taken from the meta data is often made obsolete due to the change in tastes of music, it was necessary to provide a possibility of generating meta data directly from the musical properties of a piece of music shortly before classification, wherein a classification of the piece of music then need not be stored in the meta data, but wherein only the musical and/or the music-theoretical properties of the piece of music are recognized from the piece of music itself, and wherein the style of music or subclass of the style of music of the piece of music may be inferred therefrom.
As an evident characterizing feature of a piece of music, the classification of occurring types of chords, such as a D major or a G minor chord in a piece of music, could serve as an important feature in classifying the piece of music to belong to a style of music or subclass of a style of music. In a first approach of recognizing a key of a piece of music, David Temperley suggested, in his document “The Recognition of Basic Musical Structures”, The MIT Press, 2001, pages 173 to 187, to establish key profiles by means of an empirical psycho-acoustic reference model formation. These key profiles then indicate a frequency of how often a certain note occurs, for example in a piece of music in C major, in relation to other notes. Such key profiles are represented, for example, for the C major key in FIG. 5A and for the D minor key in FIG. 5B. If a piece of music to be examined is to be classified, the time durations of music of the individual halftones (for example C, C sharp, D, . . . ) occurring in this piece are evaluated using a histogram, and are correlated with the key profiles for the individual keys, a correlation coefficient being determined. Subsequently, the piece of music to be examined is classified to belong to that key which yields the highest correlation coefficient of the histogram resulting from the piece of music to be examined, and the respective key profile.
However, such an approach has the disadvantage that a temporally long segment of a piece of music is to be used for creating a meaningful histogram as a meaningful test signal vector), and that the key of the piece of music may change within this time segment of the piece of music to be examined. This will subsequently lead to an inaccurate classification of the piece of music. In addition, it is only the key of the piece of music (and/or of the examined time segment of the piece of music) that can be recognized by the above-described method; the recognition of the key of an individual chord is thus not ensured. This primarily results from the fact that, for short time segments, no meaningful histogram may be prepared due to the short time duration of the segment. Thus, the temporal resolution behavior of the above-described method is limited.
Thus, it is the object of the present invention to provide a possibility of determining a type of chord underlying a test signal, it being intended for the determination of the chord type underlying the test signal to provide a temporal resolution which is better than has been possible in the prior art.